Following the meeting, ahead of next week’s crunch summit in Brussels, the government Chief Whip Julian Smith insisted ministers were fully behind Mrs May’s negotiating strategy.

“We are conducting an extremely tough negotiation.

“The prime minister is doing an exceptional job and everybody is behind her,” he told reporters.

It was reported, however, that a number of ministers, including Foreign Secretary Jeremy Hunt, Brexit Secretary Dominic Raab, Environment Secretary Michael Gove and International Trade Secretary Liam Fox, raised concerns during a meeting lasting around an hour and a half.

Earlier, amid speculation possible of ministerial resignations, the Work and Pensions Secretary Esther McVey, who was not at the meeting, pointedly refused to endorse the prime minister’s Chequers blueprint for Brexit.

Asked by the BBC to offer her backing to Mrs May’s plan, Ms McVey sidestepped the questions.

She said: “I am completely supportive of the prime minister.”

With the negotiations coming to a head, the central focus of the discussions is thought to have been the issue of the Northern Ireland “backstop” intended to ensure there is not return of a “hard border” with the Republic.

The EU wants Northern Ireland effectively to remain in the single market and the customs union to avoid the need for customs checks until there is a final free trade deal between the United Kingdom and the European Union.

Mrs May insists that such an arrangement must apply to the whole of the UK to avoid the creation of a “border in the Irish Sea” between Northern Ireland and the rest of the United Kingdom.

However Tory Brexiteers fear that she is about to concede to EU demands that it must be open-ended, despite previous assurances from ministers it would have to be time-limited.

Without a time limit, critics say Britain could be tied to the EU indefinitely unable to negotiate free trade deals with other countries.

Boris Johnson has said it would reduce the UK to a “permanent EU colony”.

Following three days of talks with key figures in Brussels, Mrs Foster, whose party’s 10 MPs prop up the government at Westminster, said that the DUP could not accept the EU proposals as they currently stood.

“The prime minister is a unionist.

“Many of her cabinet colleagues have assured me of their unionism,” she said.

“Therefore, they could not in good conscience recommend a deal which places a trade barrier on United Kingdom businesses moving goods from one part of the Kingdom to another.”

Her latest shot across the bows came after the party had earlier made clear that it would be prepared to vote against the Budget and other domestic legislation if Mrs May crossed their “red lines”.

Mr Hunt insisted ministers would not sign up to any plan which compromised the territorial integrity of the UK by imposing a “border in the Irish Sea”.